1. Field of the Invention
The present invention relates to pigment compositions which have excellent properties for various applications, particularly non-flocculating and non-crystallising properties.
2. The Prior Art
In general, useful pigments which exhibit clear colour tone and high tinting strength in various coating compositions consist of fine particles. However, when fine particles of pigment are dispersed in non-aqueous vehicles for use as, for example, offset printing inks, gravure printing inks and paints, it is difficult to obtain stable dispersions, various problems arising with regard to the preparation, and value, of the resulting product. For instance, dispersions which contain pigments consisting of fine particles are often highly viscous and thus not only is it difficult to dispense the dispersion product and transport the same, but also, in a very bad case, the dispersion product cannot be used due to gellation during storage. Furthermore, when pigments of different types are mixed, undesirable phenomena such as colour separation by flocculation and precipitation can take place and may cause the dispersion system to be uneven in colour and may also considerably lower the tinting strength in non-aqueous vehicles. There may also arise problems such as lowering of gloss and inferiority of levelling in films made from such dispersion systems.
In addition to the problem of dispersion of the pigments, some organic pigments undergo a crystallization change. Crystals of a pigment which are unstable (from an energy viewpoint) change their sizes and form into those of a more stable state in a non-aqueous vehicle such as is used for offset printing inks, gravure printing inks and paints. This may naturally reduce the commercial value of the dispersion system, due to a remarkable change in colour tone, reduction of tinting strength and formation of coarse particles.
There have been a number of proposals to improve non-flocculation and crystal stability of pigments, particularly copper phthalocyanine pigments and quinacridone pigments.
Such proposals may be broadly classified from a technical point of view into the following two categories. The first category includes proposals for coating the surfaces of pigment particles with colourless compounds, such as silicon oxide, aluminium oxide and tert-butyl benzoate as disclosed in U.S. Pat. Nos. 3,370,971 and 2,965,511. The second category includes, as typically described in Japanese Pat. No. 41-2466 and U.S. Pat. No. 2,761,868, processes of admixing the pigments with compounds which are obtained by introducing into organic pigments, as a matrix skeleton, substituents (on side chains) such as a sulfo group, a sulfonamide group, an aminomethyl group, a phthalimidemethyl group and the like.
The processes of the second category are better than those of the first category, in that the second category of processes can provide better non-flocculation and crystal stability in a non-aqueous vehicle and ensure easy preparation of pigment compositions. However, the non-flocculation and crystal stability thereby obtained are not adequate.
Further, with respect to processes for mixing azo compounds, Japanese Pat. Nos. 45-11026 and 53-35090 disclose methods in which alkaline earth metal sulfonates and organic amine salt of azo dyes are admixed. However, the effects obtained by such methods are also inadequate.
Little work has been carried out with respect to pigments such as dioxazine, anthrapyrimidine, anthanthrone, indanthrone, flavanthrone, perynone, perylene, thioindigo and 4,4'-diamino-1,1'-dianthraquinonyl.